Unfired pressure vessel



United States Patent Oflice 3,107,997 UNFIRED PRESSURE VESSEL Roland A. Kozlik, Livingston, and .Charles I. Novak, Scotch Plains, N.J., assignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware 1 Filed July 31, 1961, .Ser. No. 128,218

11 Claims. (Cl. 75-124) s The present invention relates to austenitic stainless steels and, more particularly, to nickel-containing stainless steels and the manufacture of structures therefrom.

It is well known that extra-low carbon grades of nickel-containing stainless. steels have many metallurgically attractive advantages which have led to their adoption'in many areas of manufacturing. However, for the production of unfired pressure vessels for use up to and above 800 F., these grades of stainless steels have substantially limited commercial utilization since the engineering boiler codes have imposed extremely severe stress penalties attendant their use and, as a matter of fact, do not authorize the use of certain grades of stainless steel for unfired pressure vessels operating at temperatures in excess of 800 F. These officially imposed stress penalties are based in part upon a recognition that steels within the normally accepted composition limits for low and extra-low carbon stainless steels have widely varying high temperature stress characteristics which could not heretbfore with certainty be predicted. In view of this fact, the extra-low carbon grades of nickel containing stainless steels ,are not now commercially accepted for use in unfired pressure vessels operating at temperatures of the order of 500 F. to 800 F. or higher, regardless of whatever other attractive advantages may be afforded by the alloys. Although many attempts were made to provide extra-low carbon stainless steels which can be employed in unfired pressure vessels used at high temperatures, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that by maintaining specified and coordinated ranges of elements inherently copresent with nickel, chromium and iron in commercially produced stainless steels in a further coordinated rela- 'tions-hip with specified amounts of alloying ingredients, stainless steels can be provided which are particularly suited for the manufacture of pressure vessels employable at elevated temperatures.

I It is an object of the present invention to provide a novel stainless steel pressure vessel for use at elevated temperatures of the order of 800 F. and higher.

Another object of the invention is to provide a novel and improved method for the production of stainless steel structures such as pressure vessels utilizable at temperatures of the order of 800 F. and higher.

The invention also contemplates providing a unique stainless steel particularly adapted to be employed in the construction of pressure vessels utilizable at temperatures of the order of 800 F. and higher.

' Other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawing which is a graphical plot of the effective factor of an alloy .as hereinafter defined versus the boron content thereof.

Generally speaking, the present invention contemplates the manufacture of articles, structures nad the like, such as unfired pressure vessels operable at temperatures of the order of about 800 F. to about 1200 F., from wrought alloys consisting essentially in weight percent of about 8% to about 14% nickel, about 15% to about 21% chromium, about 0.0015% to about 0.03% boron, about 0.008% to about 0.08% nitrogen, up to about 2% man- 3,107,997 Patented Oct. 22, 1963 silicon, with the balance being essentially iron together with correlated and controlled amounts of one or more of the elements columbium, titanium, vanadium and molybdenum, in addition to closely restricted amounts of elements unavoidably present as impurities in commercially manufactured stainless steels. The alloys from which the articles of the present invention are formed by working techniques including rolling, forging, extrusion and the like are adjusted while molten prior to casting to contain up to about 0.25% columbium, up to about 0.2% vanadium, up to about 0.25 titanium and up to about 1% molybdenum. The wrought alloys operable in accordance with the present invention are stably austenitic and can contain silicon in amounts up to 1%, for example, about 0.4% to about 0.9%, but the silicon content is advantageously so controlled that when the alloy contains less than about 0.02% carbon, 10% nickel and 0.03% nitrogen, the sum of the percentages of silicon and chromium does not exceed about 19.8%.

In the manufacture of the articles of the present invention and, in particular, when manufacturing said articles by hot working an air melted alloy which contains at least about 0.02% nitrogen, less than about 0.01% titanium and advantageously less than about 0.03% carbon, care must be taken to avoid excessive amounts of contaminating impurities during all stages of manufacture including melting, casting, working, welding, machining and the like. Low melting metals suchas lead should be held to an absolute minimum in the alloy composition. Thus, lead which can be picked up during melting, casting, etc., should be present in the alloy of the finished article in amounts no greater than, for example, about 0.01%. Tin and zinc should likewise be maintained at as low a level as is commercially practical. Phosphorus and sulfur advantageously are maintained at a maximum of about 0.02% each. Zirconium in the alloy of the finished article should be no greater than about 0.02% and, advantageously, is less than 0.01%

When making articles in accordance with the present invention, a molten bath of alloy is produced and adjusted in composition so that the alloy as cast therefrom and as subsequently worked and formed, contains interrelated amounts of nitrogen and one or more of the elements oolumbium, vanadium, titanium and molybdenum which in turn are related in a particular manner to the boron content. The effective amount of columbium and/or vanadium and/ or titanium and/or molybdenum and nitro gen in the alloy articles of the present invention termed, for convenience, the effective factor (E.F.) of the alloy, are defined by the appropriate algebraic expression set forth in Table I in which percent (when used in conjunction with a chemical symbol of an element) indicates the numerical value of the percentage by weight of said element. As indicated in Table I, the effective factor of the alloy is determined with reference to the particular contents of titanium and nitrogen in the alloy.

---0.01 to 0., K 0 to 0.1 4.9 [4% Nto percent Ti] plus K'J 0.12 to 0.22 1.5 [4% N to percent Ti minus 0.121 plus K plus 0.588. 022 0.4 [4% N to percent Ti minus 0.22] plus K plus 0.738.

1 K equals 6% Ch plus 1.9% V plus 0.0 [percent Mo minus 0.2] minus 2 [percent Cu minus 0.28]. When the uantity [percent M0 minus 0.2] or the quantity [percent Cu minus 0.2!; employed in the definitions set forth in Table I 15 equal to a negative number, it is to be disregarded and treated as equal to zero.

Table II Minimum Percent El perboron 1 cent Deterrnlncd by speetrographie analyses which analyses closely itiggroximate boron percentages added to alloy following final deoxida- This relationship between the mini-mum effective factor of the alloy and the percentage of boron is also exem plified in the drawing. Referring now thereto, it is to be observed that articles in accordance with the present invention are made from alloys which are adjusted in composition so as to be represented by a point lying to the right of the curve when the boron content is plotted against the effective factor of the alloy.

In carrying the invention into practice, it is advantageous to adjust the composition of the molten bath so that the cast alloy which is wrought into the novel articles of the present invention contains amounts of alloying in- After the molten bath of the alloy is so adjusted, the alloy is cast and wrought to form heat-resistant articles. The articles thus made in accordance with the present invention exhibit excellent high temperature stability when subjected to temperatures of the order of 800 F. to 1200" F. by virtue of the fact that they are comprised of a non age-hardenable alloy possessing a coordinated chemical composition specifically designed to minimize the formation of deleterious microstructures when subjected for extended periods of time to stress at elevated temperatures.

To illustrate more fully the advantages of the present invention, alloys illustrative of alloys which can be employed in the novel process and articles of the present invention are set forth in Table IV.

Table IV Percent by weight Element Alloy No. 1 Alloy No. 2 Alloy No. 3 Alloy No. 4 Alloy No. 5

l Bal. E. 1 Hal. E. 1 Hal. E 1 1331. E. l 13:11. E.

1 Balance essentially.

When formed into wrought articles, the alloys set forth in Table IV are ductile, weldable and exceptionally resistant to the deleterious effects of stress at elevated gredients as set forth in Table III correlated as set forth hereinbefore.

Table III Range, Percent Element Alloy C 0.15 max O 1 0015-0035..." 0.03-0.04

0.01 max 0.15 max O 1 0.1 max" 0.3 max 0.7 max Bel. E.

1 Balance essentially.

In correlating the alloying ingredients to adjust the composition of the alloy in accordance with the concepts of the present specification and claims, it is to be noted that for any given alloy range the effective factor of the alloy is defined with respect to the ranges of nitrogen and 3 and when the nitrogen-titanium factor is in excess of 0.12 the ER of the alloy is defined by the'expression temperatures of the order of 1200 F. The data in Table V shows the l00-hour rupture stress at 1200' F. in pounds per square inch (p.s. i.) of articles made from the alloys set forth in Table IV.

The data set forth in Table V is to be compared to data with regard to alloys which are similar in chemical composition but which are outside the scope of the present invention. The IOO-hou'r rupture stress of such similar alloys outside the scope of the present invention can be as low as 18,000 p.s.i. or even 15,000 psi. In addition, al-

alloy article.

loys outside the scope of the present invention can form deleterious microstructural constituents during processing or service in articles exposed to elevated temperatures. Thus, if the articles contain too much chromium, molybdenum and/or silicon and/or too little nickel, carbon and/or nitrogen, deleterious amounts of ferrite can form in the substantially completely austenitic matrix of the Excessive amounts of columbium, molybdenum and titanium can induce the formation of deleterious carbides. Excessive amounts of vanadium tend to reduce ductility and increase the tendency of the alloy articles to be notch sensitive. When nitrogen is present in the alloy in amounts in excess of about 0.01%, amounts of titanium in excess of about 0.01% are to be avoided in order to minimize and/ or eliminate the formation of deleterious amounts of titanium nitrides and/ or carbonitrides. To minimize the formation of deleterious amounts .of carbides, the carbon content of the alloy articles of the present invention must not exceed 0.15%, should not exceed about 0.10% or 0.08% and, advantageously, is less than 0.03%. Excessive amounts of aluminum over 0.2% can weaken the alloy articles of the present invention. Excessive amounts of boron can induce undue difficulties in welding said articles but advantageously at least about 0.002% boron is present in the alloys. When producing the alloy articles in accordance with the present invention, small amounts of cobalt can be introduced along with nickel and small amounts of tantalum can be introduced along with columbium. Such small incidental amounts of cobalt and tantalum are not deleterious to the characteristics of the alloy articles of the present invention.

Alloy articles made in accordance with the present invention and adapted to be employed at temperatures of the order-of 800 F. and higher, exhibit 100-hour rupture stresses at least in excess of 30,000 p.s.i. at 1200 "F. Such alloy articles include hydrogenation equipment, high temperature oil and steam piping, superheater elements, furnace parts such as retorts, mufiles, radiant tubes, mesh belts, chain link belts, etc., heat exchangers, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. An unfired pressure vessel for use at temperatures of about 800 F. to about 1200 F. made of a stable,-

non-age hardenable austenitic alloy consisting essentially of about 8% to about 14% nickel, about 15% to about 21% chromium, about 0.0015% to about 0.03% boron, about 0.008% to about 0.08% nitrogen, up to about 2% manganese, up to about 0.15% carbon, up to about 0.2% aluminum, -up to about 0.25% titanium, up to about 0.5% copper, up to about 1% silicon, up to about 0.25% columbium, up to about 0.2% vanadium, up to about 1% molybdenum with the balance being essentially iron, the elements in said alloy being so correlated that when the effective factor of said alloy is plotted against the boron content thereof, the alloy is representable by a point lying to the right of the curve in the accompanying drawing.

2. An unfired pressure vessel in accordance with clai 1 made of an alloy containing up to about 0.08% carbon.

3. An unfired pressure vessel in accordance with claim l madc of an alloy containing less than about 0.01% titanium.

4. An unfired pressure vessel in accordance with claim 1 made of an alloy containing up to about 0.035% carbon.

5. An unfired pressure vessel in accordance with claim 4 made of an alloy containing less than about 0.01% titanium. I

6. An unfired pressure vessel in accordance with clairr 4 made of an alloy containing at least about 0.002% boron.

7. An unfired pressure vessel for use at temperatures 01 about 800 -F. to about 1200 -F. made of a stable, nonage hardenable austenitic alloy consisting essentially 01 about 9% to about 12% nickel, about 16% to about 19% chromium, about 0.0015 to about 0.003% boron. about 0.03% to about 0.04% nitrogen, about 1% tc about 2% manganese, about 0.015% to about 0.035% carbon, up to about 0.1% aluminum, up to about 0.01% titanium, up to about 0.3% copper, about 0.3% to about 0.9% silicon, about 0.1% to about 0.15% columbium, up to about 0.15% vanadium, up to about 0.7% molybdenum with the balance being essentially iron, the ele' ments in said alloy being so correlated that when the effective factor of said alloy is plotted against the boron content thereof, the alloy will be represented by a point lying to the right of the curve in the accompanying drawmg.

8. An unfired pressure vessel for use at temperatures of about 800 F. to about 1200 F. made of a stable, nonage .hardenable austenitic alloy consisting essentially of about 9% to 12% nickel, about 16% to 19% chromium, about 0.01% to about 0.25% boron, about 0.03% tc about0.04% nitrogen, about 1% to about 2% manganese. about 0.015 to about 0.035% 'carbon, up to about 01% aluminum, up to about 0.01 titanium, up to about 0.3% copper, about 0.3% to about 0.9% silicon, up to about 0.15 columbium, up to about 0.15 vanadium, up tc about 0.7% molybdenum with the balance being essentially iron, the elements in said alloy being so correlated that when the effective factor of said alloy is plotted against the boron content thereof, the alloy will be represented by a point lying to the right of the curve in the accompanying drawing. a

9. An unfired pressure vessel for use at temperature: of about 800 F. to'about 1200 F. made of a stable nonage hardenable austenitic alloy consisting essentially 01 about 9% to about 12% nickel, about 16% to about 19% chromium, about 0.0015 to about 0.003% boron, about 0.01% to about 0.04% nitrogen, about 1% to about 2% manganese, about 0.015% to about 0.035% carbon up to about 0.1% aluminum, up to about 0.04% titanium. up to about 0.3% copper, about 0.3% to abou 0.9% silicon, about 0.1% to about 0.15% columbi m, abou 0.1% to about 0.15% vanadium, up to about 0.7% molybdenum with the balance being essentially iron, the elements in said alloy being so correlated that when the effective factor of said alloy is plotted against the boror content thereof, the alloy will be represented by a point lying to the right of the curve in the accompanying drawing.

10. An unfired pressure vessel for use at temperature: of about 800 Frto about 1200 F. made of a stable, nonage' hardenable austenitic alloy consisting essentially 01 about 9% to about 12% nickel, about 16% to abou 19% chromium, about 0.003% to about 0.025% boron about 0.01% to about 0.04% nitrogen, about 1% tr about 2% manganese, about 0.015%' to about 0.035% carbon, up to about 0.1% aluminum, up to about 0.1% titanium, up to about 0.5% copper, about 0.3% to abou 0.9% silicon, about 0.1% to about 0.15% columbium about 0.10% to about 0.15% vanadium, up to abou 0.7% molybdenum with the balance being essentially iron, the elements in said alloy being so correlated tha when the effective factor of said alloy is plotted agains the boron content thereof, the alloy will be representet by a point lying to the right of the curve in the accom panying drawing.

about 0.1% to about 0.15% columbium, up to about 10 0.15% vanadium, up to about 0.7% molybdenum with the balance being essentially iron, the elements in said alloy being so correlatedthat when the etfective factor of said alloy is plotted against the boron content thereof, the

alloy will be represented by a point lying to the right of 5 the curve in the accompanying drawing.

References Cited in the fiie of this patent UNITED STATES PATENTS 2,562,854 Binder July 31, 1951 2,602,028 Urban et a1. July 1, 1952 2,750,283 Loveless June 12, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,107,997 October 22 1963 Roland A. Kozlik et 31.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column, 1, line 66, for "nad" read and column 2 lines 60 to 68, Table I, should appear as shown below instead of as in the patent:

4% N Ti Q Effective Factor -0.01 Z 7.8 Ti 4% N 0.01 K* -0.01 to 0 Q K* 0 to 0. 12 4.9 [4% N Ti} K* 0. 12 to 0.22 S 1.5 [4% N Ti 0. 12] 1 0.588

% Ti "0.,22] K* O 738 loo no column 6, line 30, for "0.25%" read 0.025%

Signed and sealed this 12th day of May 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER At testing Officer Commissioner of Patents 

1. AN UNFIRED PRESSURE VESSEL FOR USE AT TEMPERATURES OF ABOUT 800*F. TO ABOUT 1200*F. MADE OF A STABLE, NON-AGE HARDENABLE AUSTENITIC ALLOY CONSISTING ESSENTIALLY OF ABOUT 8% TO ABOUT 14% NICKEL, ABOUT 15% TO ABOUT 21% CHROMIUM, ABOUT 0.0015% TO ABOUT 0.03% BORON, ABOUT 0.008% TO ABOUT 0.08% NITROGEN, UP TO ABOUT 2% MANGANESE, UP TO ABOUT 0.15% CARBON, UP TO ABOUT 0.2% ALUMINUM, UP TO ABOUT 0.25% TITANIUM, UP TO ABOUT 0.5% COPPER, UP TO ABOUT 1% SILICON, UP TO ABOUT 0.25% COLUMBIUM, UP TO ABOUT 0.2% VANADIUM, UP TO ABOUT 1% MOLYBDENUM WITH THE BALANCE BEING ESSENTIALLY IRON, THE ELEMENTS IN SAID ALLOY BEING SO CORRELATED THAT WHEN THE EFFECTIVE FACTOR OF SAID ALLOIY IS PLOTTED AGAINST THE BORON CONTENT THEREOF, THE ALLOY IS REPRESENTABLE BY A POINT LYING TO THE RIGHT OF THE CURVE IN THE ACCOMPANYING DRAWING. 